Fix some more image rendering occurrences

plugins/Toolbox/resources/qml/ToolboxAuthorPage.qml

@@ -1,7 +1,7 @@
 // Copyright (c) 2018 Ultimaker B.V.
 // Toolbox is released under the terms of the LGPLv3 or higher.
 
-import QtQuick 2.2
+import QtQuick 2.3
 import QtQuick.Controls 1.4
 import QtQuick.Controls.Styles 1.4
 import UM 1.1 as UM
@@ -32,6 +32,7 @@ Item
             height: UM.Theme.getSize("toolbox_thumbnail_medium").height
             fillMode: Image.PreserveAspectFit
             source: details.icon_url || "../images/logobot.svg"
+            mipmap: true
             anchors
             {
                 top: parent.top

plugins/Toolbox/resources/qml/ToolboxDetailPage.qml

@@ -1,7 +1,7 @@
 // Copyright (c) 2018 Ultimaker B.V.
 // Toolbox is released under the terms of the LGPLv3 or higher.
 
-import QtQuick 2.2
+import QtQuick 2.3
 import QtQuick.Controls 1.4
 import QtQuick.Controls.Styles 1.4
 import UM 1.1 as UM
@@ -33,6 +33,7 @@ Item
             height: UM.Theme.getSize("toolbox_thumbnail_medium").height
             fillMode: Image.PreserveAspectFit
             source: details.icon_url || "../images/logobot.svg"
+            mipmap: true
             anchors
             {
                 top: parent.top

plugins/Toolbox/resources/qml/ToolboxDownloadsShowcaseTile.qml

@@ -1,7 +1,7 @@
 // Copyright (c) 2018 Ultimaker B.V.
 // Toolbox is released under the terms of the LGPLv3 or higher.
 
-import QtQuick 2.2
+import QtQuick 2.3
 import QtQuick.Controls 1.4
 import QtQuick.Controls.Styles 1.4
 import UM 1.1 as UM
@@ -40,6 +40,7 @@ Item
             height: UM.Theme.getSize("toolbox_thumbnail_large").height - 2 * UM.Theme.getSize("default_margin").height
             fillMode: Image.PreserveAspectFit
             source: model.icon_url || "../images/logobot.svg"
+            mipmap: true
         }
     }
     Label